1. Field of the Invention
The present invention pertains to fiber filtration tubes for use in erosion and sediment control.
2. Background Art
Fiber mulch mats are in widespread use in preventing soil erosion and to aid in germination of seed beds. The fibers in such mats, also termed turf reinforcement mats (“TRM”) may be derived from numerous organic sources, including wood fibers, straw, jute, sisal, coconut, and paper. Due to its ready availability, wood fibers are preferred for such products.
Fiber mulch mats must possess satisfactory physical characteristics which are often conflicting. For example, the mats should aid in water retention when used to aid seed germination, yet must be open enough to allow seedlings to penetrate the mat. The mats must also be of sufficient strength to be handled effectively during installation over soil and/or seedbeds, and must retain their integrity over extended periods while exposed to the elements. Otherwise, their ability to control run-off, and hence erosion, would be rapidly lost.
In the past, fiber mats have been bound together with the aid of numerous organic binders, both natural and synthetic. Natural binders include starches, vegetable gums, and the like, including chemically modified celluloses such as hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, and the like. Such natural or chemically modified natural binders suffer from the defect of rapid degradation due to exposure and to the action of microorganisms. Synthetic polymeric binders such as styrene-butadiene latexes, polyacrylates, polyvinylacetate, polyvinylacetate-ethylene copolymers, phenolic resins, and the like have also been used. Such polymer-based binders are generally more expensive than natural binders, and many exhibit at least modest water swellability, which decreases the binding capability and hence strength of the product over time following installation.
In U.S. Pat. No. 5,779,782, binding of spray-applied fiber mulch mats is improved by the incorporation of crimped synthetic fibers which serve to entangle with other crimped synthetic fibers and natural fibers to increase the integrity of spray applied mats while employing less or no binder. In U.S. Pat. No. 6,360,478, it is proposed to employ permanently crimped natural fibers for a similar purpose. No preformed mats are disclosed, however, and the degree of entanglement of either natural or synthetic fibers, without the use of a binder, may not be sufficient to formulate a mat with adequate tear strength or tensile strength. In U.S. Pat. Nos. 5,779,782, 5,330,828 and 5,484,501, it is proposed to employ low melting organic polymer fibers together with natural mulch fibers. The mat is preferably air laid, and passes between heated embossing rollers which melt portions of the organic fibers, thus binding together the mulch fibers.
Control of surface runoff to prevent erosion has been practiced for millennia. Use of terraced hillsides for agriculture, and construction of low stone walls on hills and in ditches to trap sediment and reduce runoff are widely evident throughout the world. However, erosion control mats do not always work well alone on steep slopes, and are generally impractical to install over large areas. Moreover, areas where crops are being planted and grown must be kept free of such products. Finally, while the erosion control mats previously described can be effective to reduce water velocity and trap larger sediment to a degree, they are largely ineffective at trapping very fine particulates such as colloidal clay particles.
Recently, wattles have been employed to reduce water velocity of surface runoff and to trap sediment. These wattles are essentially mesh tubes filled with natural fibers such as rice straw, wheat straw, coconut, and wood excelsior fibers. The wattles or fiber rolls are placed at intervals across the slope, i.e. perpendicular to the direction of runoff, and are frequently used in conjunction with rolled erosion control products and hydraulic seeding techniques, as described in PCT/US04/14464, herein incorporated by reference.
When employed to trap fine sediment, such fiber rolls may also be termed “filtration tubes.” However, tubes specifically designed to trap and flocculate fine sediment have not been commercially available; what “filtration” occurs has been incidental to commercial wattles or fiber rolls whose principle purpose is preventing washout, lowering the velocity of water runoff, and trapping large sediment particles. A disadvantage of conventional fiber rolls or wattles is their relatively high transportation cost, as their density is rather low, and as they can tolerate little compression to facilitate shipping. A further disadvantage is their limited lifespan. The natural fibers tend to degrade rather quickly, in most cases within a year or two. Use of rice straw, with its relatively high silica content, can extend the useful lifetime, claimed to be up to 3 to 5 years in the low humidity, semi-arid western North American environments. In addition to their use on sloped surfaces, filtration tubes can also be positioned in gullies, channels and ditches.
The sediment holding capacity and filtration capacity are related to numerous properties, including the geometric shape of the filtration tube, composition of the fill material and the fill density. A high fill density may result in more efficient capture of very fine particles such as those found in clay and clayey soils. However, the tradeoff is that such higher packing density both lowers the water filtration rate, which results in overflow under high rainfall conditions and may also causes the tubes to become plugged with sediment particles, losing much of their effectiveness, again resulting in overflow. Conventional straw fiber rolls also do not absorb water easily due to the high lignin content and shape of the rice straw fibers as well as the limited surface area per unit weight of such products. Washout of newly installed straw and wood excelsior fiber rolls can occur due to their light weight and inability to absorb large amounts of water. Colloidal particles, in general are very inefficiently trapped by all such products.
It would be desirable to provide a fiber filtration tube suitable for use in erosion control, particularly in applications where fine particles such as those present in clayey soils are present, which provide superior sediment retention capability, and which are effective even when high concentrations of fine sediment are present. It would be further desirable to provide an economical means of providing such fiber filtration tubes, particularly those of relatively long length.